The present invention pertains to a process for preparing dispersions of particles, especially aqueous dispersions. These dispersions may be used in the preparation of aqueous inkjet inks, pigmented paints, pharmaceuticals, agricultural products, etc. More particularly, the invention relates to a dispersion process where a polar solvent is added during the dispersion process such that the hydrogen bonding solubility parameter component, δh, of the initial dispersion mixture increases at least 1.5 units.
Dispersion methods are commonly used to disperse particles. A variety of dispersion processes have been described for dispersing particles. For ink jet inks pigments are dispersed with polymeric dispersants. One such process is the two-roll mill preparation of polymer dispersed pigments for ink jet inks as described in U.S. Pat. No. 5,310,778.
A media mill dispersion using plastic substantially cubic media is described in US20030089277.
US20050009977 describes obtaining a pigment treated with water insoluble vinyl polymer particles in an aqueous solvent and then removing the solvent.
U.S. Pat. No. 6,723,705 describes a process for obtaining an aqueous dispersion of pigment containing polymer particles with a key step being the removing the solvent to obtain a solvent-removed product.
U.S. Pat. No. 6,866,707 describes two processes to obtain a polymer/pigment system; 1) a phase inversion emulsification where water is added to a mixture of polymer and pigment resulting in a phase inversion; 2) a pH change system where a pigment dispersed with a resin (polymer) is neutralized with a basic compound to shift the pH to fix the resin onto the pigment.
U.S. Pat. No. 6,924,035 describes a process in which a combination of solvents is used and a polymer is precipitated form the mixture of solvents onto the finely dispersed pigment particles.
There is still need for improved dispersion processes, especially for the production of colorant dispersions for high performance end use applications such as ink jet ink and exterior paints for vehicles such as automobiles and trucks.
None of the above publications disclose dispersing processes or other polymer/pigment processing steps that describe a dispersion process where a polar solvent is added during the dispersing process such that the hydrogen bonding solubility parameter component of the initial dispersion mixture increases at least 1.5 units. It has been discovered that these polymer dispersed pigments have a better balance of properties to permit formulating latitude in the ink jet inks and can produce improved optical properties.